Optical fiber technology is a core technology for long-distance communication systems. Recently, it has been also applied in short-distance communication systems such as interconnection between systems, or short-distance networks. This progress is achieved via the implementation of a vertical-cavity surface emitting laser (VCSEL). Compared with an edge-emitting laser, the size of the vertical-cavity surface emitting laser is reduced with less power consumption. The greatest benefit of VCSEL is its low fabrication cost. VCSEL can be tested on wafers so that any failed devices can be found before packaging to save the production cost.
Erbium doped optical amplifiers have been used for many years in optical telecommunications networks to boost the strength of an optical signal as it is transmitted along a fiber. While there are many different types of these amplifiers, they all typically rely on relatively expensive narrow-band lasers as the pumping sources. It has been recently shown that in some specially prepared erbium doped optical waveguides, such as silica layers containing Si nanocrystals or nanoclusters dispersed in the erbium doped glass matrix, that the erbium can be efficiently excited using light sources which emit over a broad wavelength range in the near-infrared or visible portion of the electromagnetic spectrum. Light emitting diodes (LEDs) have been used as a low cost pumping source for these types of amplifiers as there is no longer a strict requirement on the pumping wavelength as is the case in standard erbium doped glass. Such an arrangement has been discussed in a paper by Jinku Lee and Jung H. Shun entitled “Optical gain at 1.5 microns in nanocrystal Si sensitized erbium doped silica waveguide using top-pumping 470 nm LEDs” presented at the 2004 OFC meeting. Here an array of LEDs was used to pump a section of erbium doped silica waveguide, which had been sensitized with Si nanocrystals.
However, as in the case above, the much lower radiance of the LED, compared to a laser, places a limitation on the efficiency in which the pump power can be transferred to the active medium of the waveguide and consequently on the output power of the amplifier. Thus for a given length of fiber in a communications network, more LED based amplifiers would be required thereby negating any cost savings over laser based amplifiers.
In general, the prior art taught self-imaging waveguide amplifiers, photopumped VCSELS and Semiconductor Coupled Optical Waveguide Lasers (SCOWL). However, none of the prior art provide, for a optically-pumped, semiconductor waveguide amplifier, high power with diffraction limited beams and very high efficiency over a wide range of wavelength.